Initial commit: standalone quiz-testing system

Full-stack F# (Domain/Server/Client via Fable+Elmish+Feliz), PostgreSQL
persistence via Dapper, Docker Compose deployment. Student quiz-taking flow
with time-limit enforcement and focus-loss tracking, Teacher question bank
and quiz builder with results analytics, Admin user management.

src/Client/Shared/JsonWire.fs

@@ -0,0 +1,71 @@
+module Client.Shared.JsonWire
+
+// Fable.Remoting.Client pulls in Fable.Remoting.MsgPack, whose `inline`
+// helpers reference private functions in a way the current Fable compiler
+// rejects at build time. Until that's fixed upstream, each feature's `Api.fs`
+// talks to its own plain Giraffe route by hand, using the helpers below to
+// POST/GET JSON and decode the {"Ok": ...} / {"Error": ...} shape
+// Fable.Remoting.Json already produces on the server (see `Server/Json.fs`).
+open Fable.Core
+open Fable.Core.JsInterop
+open Domain
+
+let private serverUrl = "http://localhost:5144"
+
+[<Emit("Object.prototype.hasOwnProperty.call($0, $1)")>]
+let hasKey (_o: obj) (_key: string) : bool = jsNative
+
+[<Emit("fetch($0, $1).then(r => r.json())")>]
+let private fetchJson (_url: string) (_init: obj) : JS.Promise<obj> = jsNative
+
+/// `body = None` for GET-style calls with no request payload.
+let callApi (token: string option) (httpMethod: string) (path: string) (body: obj option) : Async<obj> =
+    async {
+        let headers =
+            match token with
+            | Some t -> createObj [ "Content-Type" ==> "application/json"; "Authorization" ==> ("Bearer " + t) ]
+            | None -> createObj [ "Content-Type" ==> "application/json" ]
+
+        let baseFields = [ "method" ==> httpMethod; "headers" ==> headers ]
+
+        let fields =
+            match body with
+            | Some b -> baseFields @ [ "body" ==> JS.JSON.stringify b ]
+            | None -> baseFields
+
+        return! fetchJson (serverUrl + path) (createObj fields) |> Async.AwaitPromise
+    }
+
+// ---- Id encode/decode: wire shape is {"CaseName": "<guid>"} ----
+
+let encQuizId (QuizId g) : obj = createObj [ "QuizId" ==> string g ]
+let encTopicId (TopicId g) : obj = createObj [ "TopicId" ==> string g ]
+let encUserId (UserId g) : obj = createObj [ "UserId" ==> string g ]
+let encAttemptId (AttemptId g) : obj = createObj [ "AttemptId" ==> string g ]
+let encQuestionId (QuestionId g) : obj = createObj [ "QuestionId" ==> string g ]
+let encOptionId (OptionId g) : obj = createObj [ "OptionId" ==> string g ]
+
+let decUserId (o: obj) : UserId = UserId(System.Guid.Parse(o?UserId: string))
+let decTopicId (o: obj) : TopicId = TopicId(System.Guid.Parse(o?TopicId: string))
+let decQuizId (o: obj) : QuizId = QuizId(System.Guid.Parse(o?QuizId: string))
+let decQuestionId (o: obj) : QuestionId = QuestionId(System.Guid.Parse(o?QuestionId: string))
+let decOptionId (o: obj) : OptionId = OptionId(System.Guid.Parse(o?OptionId: string))
+let decAttemptId (o: obj) : AttemptId = AttemptId(System.Guid.Parse(o?AttemptId: string))
+
+let optToJs (mapper: 'a -> obj) (opt: 'a option) : obj =
+    match opt with
+    | Some x -> mapper x
+    | None -> null
+
+let optDec (mapper: obj -> 'a) (raw: obj) : 'a option =
+    if isNullOrUndefined raw then None else Some(mapper raw)
+
+let decodeRole (raw: obj) : Role =
+    match unbox<string> raw with
+    | "Admin" -> Admin
+    | "Teacher" -> Teacher
+    | "Student" -> Student
+    | other -> failwithf "Неизвестная роль: %s" other
+
+let decodeResult (decodeOk: obj -> 'a) (raw: obj) : Result<'a, string> =
+    if hasKey raw "Ok" then Ok(decodeOk raw?Ok) else Error(unbox<string> raw?Error)